SCUFFLES broke out and police used tear gas during a mass rally in Athens yesterday as Greeks railed against government pension reforms demanded by international creditors.

Demanding an end to austerity, about 50,000 Greeks marched peacefully on parliament in central Athens chanting for the government to ditch the proposals, which many see as a betrayal of the leftist values of the Syriza party, who were elected to government last year on an anti-austerity ticket.

At the same time, services ground to a halt in a general strike that cancelled flights, ferries and public transport, shut down schools, courts and pharmacies, and left hospitals with only emergency staff.

In Athens, breaking away from the main march, black-clad youths hurled stones and petrol bombs at police, who responded with tear gas and stun grenades.

Bus stops were smashed and a car set alight during a cat-and-mouse game with police in the back streets of the city centre.

The backlash is piling pressure on leftist prime minister Alexis Tsipras, elected just over a year ago.

With just a three-seat majority in parliament, he is stuck between either pushing the reforms through to appease international creditors or attracting the wrath of thousands of Greeks.

The general strike is the most significant challenge to date to the coalition government of Tsipras.

It is the second nationwide walkout since Tsipras took power in January 2015 on a pledge to end years of austerity, after the radical left party had led opposition to pension reforms.

However, the coalition caved in under the threat of expulsion from the euro-zone and sign up to more belt-tightening reforms under an European Union-International Monetary Fund bailout package worth up to €86 billion.

“They should be strung up here, in Syntagma Square,” said pensioner Nikos Ghinis as he walked along with thousands of others. “I’m getting €740 a month for 40 years of work ... I’m [demonstrating] here for my children and grandchildren,” he added.

The 24-hour strike coincides with a major review of Greece’s performance on terms of its bailout.

The heads of the EU and IMF mission assessing Greece’s progress arrived in Athens earlier this week to discuss the pension plan, tax reforms and bad loans weighing on Greek banks.

Greek ministers were in talks with the mission chiefs in a hotel near Syntagma Square when the clashes erupted.

The government wants to conclude the review swiftly to start talks on debt relief and convince Greeks that their sacrifices are paying off after six years of austerity and a deep recession that have brought the unemployment rate to 25 per cent.

“They are raiding our souls not just our pockets,” said 70-year old George Stathopoulos. “They betrayed us.”

Greece’s economy will be the only one in the EU to shrink this year, the EU Commission said yesterday, but the fall is much smaller than previously estimated. The Greek government has promised to cut pension spending by one per cent of GDP – or €1.8bn – this year.

To protect retired people whose pensions have been slashed 11 times since 2010, the government plans to increase social security contributions by employees and employers.

But unions say the new plan will increase unemployment as the costs to hard-pressed businesses will go up and force workers, mainly the self-employed, into tax evasion as it links social security contributions to declared income.

Under the terms of pension reform, social security contributions will increase almost three-fold.